1. Field of the Invention
The present invention relates generally to a magnetic recording medium used in a magnetic record/reproduction apparatus such as a magnetic disk drive.
2. Description of the Related Art
In a recent hard disk drive, high-density recording technology has been magnificently advanced. There are two keys for improvement of recording density. One is a floating technology of a magnetic head, and the other is development of a thin-film type head.
In order to establish above technologies, it is indispensable to improve antifriction property or abrasion resistance between the magnetic head and the magnetic recording medium (i.e. a magnetic disk).
So far, a generally utilized method for starting or stopping the hard disk drive is a contact-start-stop (abbreviated as CSS) method. This CSS method is characterized by forcing the magnetic head and the magnetic disk to contact with each other and cause a frictional slide engagement when the device starts or stops the operation.
In a hard disk drive using such a CSS method, chance to cause a frictional slide engagement between the magnetic head and the magnetic disk will increase with lowering floating height of the magnetic head. It is, therefore, doubtless that reducing a floating amount of the magnetic head necessitates improvement of antifriction property or abrasion resistance between the magnetic head and the magnetic disk.
Regarding the thin-film type head, Al.sub.2 O.sub.3 TiC is generally known as a slider material thereof. Al.sub.2 O.sub.3 TiC has an extremely high hardness compared with a ferrite material used in a conventional Winchester type head. This predicts that the improvement of antifriction property or abrasion resistance between the magnetic head and the magnetic disk will be also essential for the adoption of the thin-film type head having an extremely high hardness.
A development of a surface protecting film is one of earnestly studied measures for improving the antifriction property or abrasion resistance. Especially, carbon material is generally recognized as a prospective protecting film material.
An improvement of the carbon protecting film has been recently conducted by adding hydrogen in the carbon protecting film. However, addition of hydrogen is not always effective to improve antifriction property and abrasion resistance. For example, the property is unexpectedly deteriorated depending on the crystal structure of the hydrogen-containing carbon film layer.
Furthermore, the hydrogen-containing carbon film layer is found to be inferior to the conventional carbon film layer in the adhesive strength to the magnetic film layer.
The reason is that the hydrogen-containing carbon film layer is fundamentally different from the conventional carbon layer in their film properties. More specifically, the conventional carbon film layer has a crystal structure similar to graphite. On the other hand, the hydrogen-containing carbon film layer has a crystal structure similar to diamond. Raman spectrum makes the difference clear. A relative intensity of the Raman spectrum, which will be later explained in detail, normally becomes small when the substance has a crystal structure similar to diamond.
As the conventional carbon film layer has a graphite-like crystal structure, a magnetic film material of Co can freely diffuse into the carbon film layer. Thus, a sufficient adhesive strength is obtained on the surface between the magnetic film layer and the carbon film layer. On the contrary, the hydrogen-containing carbon film layer has a diamond-like crystal structure; therefore, the magnetic film material of Co cannot diffuse into the carbon film layer. This is why the hydrogen-containing carbon film layer has insufficient adhesive strength to the magnetic film layer.
The adhesive strength of the protecting film layer to the magnetic film layer is an important factor to improve the antifriction or abrasion resistance of the disk. If the adhesive strength to the magnetic film layer is weak or small, any excellent film layer will be peeled off by the sliding engagement of the magnetic head and may be fatally damaged as a result of peeling-off phenomenon.
Unexamined Japanese Patent Application No. 1-258218/1989 or Unexamined Japanese Patent Application No. 1-273215/1989 discloses a magnetic disk comprising a hydrogen-containing carbon film layer. These prior arts, however, fail to define an optimum range to improve antifriction property or abrasion resistance.